The electrode is in the form of a strip comprising a metal foil having a mixture of powders pressed thereon, said powders including metal powder and electrochemically active material in powder form. The strip runs continuously through an inductor as described in U.S. Pat. No. 4,514,473. The high frequency current flowing through the inductor steps up an electromagnetic field which induces electrical "eddy" currents in the strip. The heating that results therefrom sinters the metal powder which in turn imprisons the powder grains of active material.
A problem which arises in this type of application is achieving sintering of the metal grains without thermally decomposing the grains of active material.
If inductors are used of the type described in U.S. Pat. No. 3,444,346, a satisfactory result is not obtained since the time required for sintering is such that the active material is heated for too long and is damaged.
If a hairpin-shaped inductor is used having its branches on either side of the strip running perpendicularly to the direction of strip displacement, as described in German patent application No. DE 30 15 981, it is observed that although the temperature obtained in the central part of the strip is satisfactory for obtaining good quality sintering, the edges of the strip are overheated because of edge effects. This gives rise to several drawbacks. Firstly the grains of active material situated in the vicinity of the edges are damaged, and the yield or efficiency of the electrode is reduced. Secondly, certain additives, such as cadmium, are completely unuseable since they sublime at the temperature levels reached. This also pollutes the environment.
In order to avoid these drawbacks, proposals have been made to cool the edges of such strips using a gas, however this process is difficult to control and is inaccurate.
Proposals have also been made to use an inductor, for example in the form of a metal foil, capable of treating simultaneously a larger area of the strip, thereby obtaining a more uniform temperature distribution. It has been observed that such a solution is unsuitable since even though the grains of active material receive, overall, the same total energy as when using a hairpin-shaped inductor, the greater duration of the operation renders them electrochemically inactive.
The present invention therefore seeks to implement a method making it possible to control the temperature at the edges of the strip without modifying the centraI portion of the temperature profile obtained when using a hairpin-shaped inductor.